The propagation problem is the problem of explaining by the structural properties of the swinging system what the character of the swings would be in… - Ragnar Frisch

I have insisted that econometrics must have relevance to concrete realities, otherwise it degenerates into something which is not worthy of the name econometrics, but ought rather to be called playometrics.

Personally, I never met . I saw him once when he delivered a lecture in Oslo, but being an unassuming student at the time, I did not have the courage to talk to him. So my knowledge of his theory came only through his writings. That, however, was a very intense and absorbing form of making his acquaintance. Already from my early student days, I read his writings (in German and Swedish) avidly. And I continued to do so later. When I started my study on Wicksell, I found that his works were not easy reading. Often it was only at the third or fourth reading that I grasped his ideas. Invariably, each new reading made me more and more enthusiastic. Sometimes it happened that I thought I had finally caught him in an inconsistency or in unclear thinking. Every time this happened, it turned out, however, that the error was mine.

When we approach the study of business cycle with the intention of carrying through an analysis that is truly dynamic and determinate in the above sense, we are naturally led to distinguish between two types of analyses: the micro-dynamic and the macro-dynamic types. The micro-dynamic analysis is an analysis by which we try to explain in some detail the behaviour of a certain section of the huge economic mechanism, taking for granted that certain general parameters are given. Obviously it may well be that we obtain more or less cyclical fluctuations in such sub-systems, even though the general parameters are given. The essence of this type of analysis is to show the details of the evolution of a given specific market, the behaviour of a given type of consumers, and so on.